If life has ever existed on ancient Mars, it is not on the surface, but at a depth of several kilometers below it. The new study suggests that the most inhabited part of Mars in the past, probably, were its subsoil.
The study, published on Wednesday in the journal Science Advances, showed that although Mars may have been warmer and full of water 4 billion years ago, it was still too cold and dry to live on the surface.
Four billion years ago, our Sun was much weaker – about 30%. Over time, it became warmer and lighter. If so, then ancient Mars was not the right place to live. Today, Mars receives only about 43% of the concentrated sunlight that the Earth receives from the Sun. This means that the temperature on ancient Mars barely rose from the ice melting point.
But the geological features of Mars indicate the presence of hydrated minerals and ancient river and lake beds under the surface. The researchers used various data sets to test their theory about geothermal heating on Mars billions of years ago. These data included the thickness of ice deposits in the southern Martian highlands and estimates of the annual surface temperature of the planet and the heat flux from inside to the surface 4 billion years ago.
The researchers suggested that as water penetrated deeper into Mars, any existing life could follow it many miles below the surface.